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A patient with a sore throat and fever had a throat culture revealing Gram-positive cocci in chains. The bacteria were catalase-negative. What is the most likely causative agent?
- A. Streptococcus pyogenes
- B. Staphylococcus aureus
- C. Enterococcus faecalis
- D. Micrococcus luteus
Correct Answer: A
Rationale: The correct answer is A: Streptococcus pyogenes. This bacterium fits the description of Gram-positive cocci in chains and is catalase-negative. S. pyogenes commonly causes sore throat (pharyngitis) and fever, making it the most likely causative agent in this scenario. Staphylococcus aureus (B) is catalase-positive and is not typically associated with pharyngitis. Enterococcus faecalis (C) is not typically found in chains and is rarely a cause of acute pharyngitis. Micrococcus luteus (D) is not typically associated with pharyngitis and is catalase-positive.
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The one-way transfer of genetic material from a donor cell to a recipient cell by direct cell-to-cell contact is:
- A. transformation
- B. transduction
- C. replication
- D. conjugation
Correct Answer: D
Rationale: Conjugation involves direct cell-to-cell contact for the transfer of genetic material, typically through a pilus. This process is well-documented in bacterial genetics. Transformation (A) involves uptake of free DNA from the environment. Transduction (B) is genetic transfer by a viral vector. Replication (C) is the process of producing identical copies of DNA or RNA. Therefore, the correct answer is D (conjugation) as it specifically refers to the one-way transfer of genetic material through direct cell-to-cell contact.
In which of the following GIT infections, the bacteria adhere to the intestine wall and produce toxins:
- A. Shigella spp.
- B. Enteropathogenic E.coli (EPEC)
- C. Salmonella spp.
- D. Vibrio cholerae
Correct Answer: B
Rationale: Rationale:
1. Enteropathogenic E.coli (EPEC) adheres to the intestinal wall using bundle-forming pili.
2. EPEC produces toxins that disrupt cell structure and function, leading to diarrhea.
3. Shigella spp. invade intestinal cells, Salmonella spp. invade and multiply within cells, and Vibrio cholerae produces cholera toxin causing profuse watery diarrhea.
Summary:
A, C, and D choices are incorrect because they do not specifically adhere to the intestine wall and produce toxins like EPEC does.
A 6-year-old child with suspected active tuberculosis process has undergone diagnostic Mantoux test. What immunobiological preparation was injected?
- A. Tuberculin
- B. BCG vaccine
- C. DTP vaccine
- D. Tularinum
Correct Answer: A
Rationale: The correct answer is A: Tuberculin. The Mantoux test involves injecting tuberculin, a protein derivative of Mycobacterium tuberculosis, under the skin to check for a delayed hypersensitivity reaction in individuals exposed to TB. B: BCG vaccine is a live attenuated vaccine used for TB prevention, not for diagnostic testing. C: DTP vaccine is for diphtheria, tetanus, and pertussis, not TB. D: Tularinum is not a standard immunobiological preparation used for TB testing. Therefore, A is the correct choice for the Mantoux test.
A fecal smear from a patient with severe diarrhea revealed motile Gram-negative rods with a comma shape. What is the likely causative agent?
- A. Vibrio cholerae
- B. Shigella dysenteriae
- C. Salmonella typhi
- D. Escherichia coli
Correct Answer: A
Rationale: The correct answer is A: Vibrio cholerae. This bacterium is the likely causative agent because it is known to cause severe diarrhea, and it is characterized by its motile, comma-shaped Gram-negative rods. Vibrio cholerae produces cholera toxin, leading to profuse watery diarrhea. Shigella dysenteriae causes dysentery with bloody diarrhea, Salmonella typhi causes typhoid fever, and Escherichia coli can cause various types of diarrhea but typically does not have a comma shape.
Gram (-) bacteria have basal structure consisting of:
- A. 20-25% of all materials building the cell wall
- B. 1-4% of all materials building the cell wall
- C. 4-10% of all materials building the cell wall
- D. 10-20% of all materials building the cell wall
Correct Answer: C
Rationale: The correct answer is C: 4-10% of all materials building the cell wall. Gram (-) bacteria have a thin peptidoglycan layer making up 4-10% of the cell wall. This is in contrast to Gram (+) bacteria which have a thicker peptidoglycan layer. Choice A is too high a percentage for Gram (-) bacteria. Choice B is too low as it would not provide enough structural support. Choice D is also too high and would not accurately reflect the composition of Gram (-) bacteria.